/*
 * Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */
package java.beans;

import com.sun.beans.decoder.DocumentHandler;

import java.io.Closeable;
import java.io.InputStream;
import java.io.IOException;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;

import org.xml.sax.InputSource;
import org.xml.sax.helpers.DefaultHandler;

/**
 * The <code>XMLDecoder</code> class is used to read XML documents created using the
 * <code>XMLEncoder</code> and is used just like the <code>ObjectInputStream</code>. For example,
 * one can use the following fragment to read the first object defined in an XML document written by
 * the <code>XMLEncoder</code> class:
 * <pre>
 *       XMLDecoder d = new XMLDecoder(
 *                          new BufferedInputStream(
 *                              new FileInputStream("Test.xml")));
 *       Object result = d.readObject();
 *       d.close();
 * </pre>
 *
 * <p> For more information you might also want to check out <a href="http://java.sun.com/products/jfc/tsc/articles/persistence3">Long
 * Term Persistence of JavaBeans Components: XML Schema</a>, an article in <em>The Swing
 * Connection.</em>
 *
 * @author Philip Milne
 * @see XMLEncoder
 * @see java.io.ObjectInputStream
 * @since 1.4
 */
public class XMLDecoder implements AutoCloseable {

  private final AccessControlContext acc = AccessController.getContext();
  private final DocumentHandler handler = new DocumentHandler();
  private final InputSource input;
  private Object owner;
  private Object[] array;
  private int index;

  /**
   * Creates a new input stream for reading archives
   * created by the <code>XMLEncoder</code> class.
   *
   * @param in The underlying stream.
   * @see XMLEncoder#XMLEncoder(java.io.OutputStream)
   */
  public XMLDecoder(InputStream in) {
    this(in, null);
  }

  /**
   * Creates a new input stream for reading archives
   * created by the <code>XMLEncoder</code> class.
   *
   * @param in The underlying stream.
   * @param owner The owner of this stream.
   */
  public XMLDecoder(InputStream in, Object owner) {
    this(in, owner, null);
  }

  /**
   * Creates a new input stream for reading archives
   * created by the <code>XMLEncoder</code> class.
   *
   * @param in the underlying stream.
   * @param owner the owner of this stream.
   * @param exceptionListener the exception handler for the stream; if <code>null</code> the default
   * exception listener will be used.
   */
  public XMLDecoder(InputStream in, Object owner, ExceptionListener exceptionListener) {
    this(in, owner, exceptionListener, null);
  }

  /**
   * Creates a new input stream for reading archives
   * created by the <code>XMLEncoder</code> class.
   *
   * @param in the underlying stream.  <code>null</code> may be passed without error, though the
   * resulting XMLDecoder will be useless
   * @param owner the owner of this stream.  <code>null</code> is a legal value
   * @param exceptionListener the exception handler for the stream, or <code>null</code> to use the
   * default
   * @param cl the class loader used for instantiating objects. <code>null</code> indicates that the
   * default class loader should be used
   * @since 1.5
   */
  public XMLDecoder(InputStream in, Object owner,
      ExceptionListener exceptionListener, ClassLoader cl) {
    this(new InputSource(in), owner, exceptionListener, cl);
  }


  /**
   * Creates a new decoder to parse XML archives
   * created by the {@code XMLEncoder} class.
   * If the input source {@code is} is {@code null},
   * no exception is thrown and no parsing is performed.
   * This behavior is similar to behavior of other constructors
   * that use {@code InputStream} as a parameter.
   *
   * @param is the input source to parse
   * @since 1.7
   */
  public XMLDecoder(InputSource is) {
    this(is, null, null, null);
  }

  /**
   * Creates a new decoder to parse XML archives
   * created by the {@code XMLEncoder} class.
   *
   * @param is the input source to parse
   * @param owner the owner of this decoder
   * @param el the exception handler for the parser, or {@code null} to use the default exception
   * handler
   * @param cl the class loader used for instantiating objects, or {@code null} to use the default
   * class loader
   * @since 1.7
   */
  private XMLDecoder(InputSource is, Object owner, ExceptionListener el, ClassLoader cl) {
    this.input = is;
    this.owner = owner;
    setExceptionListener(el);
    this.handler.setClassLoader(cl);
    this.handler.setOwner(this);
  }

  /**
   * This method closes the input stream associated
   * with this stream.
   */
  public void close() {
    if (parsingComplete()) {
      close(this.input.getCharacterStream());
      close(this.input.getByteStream());
    }
  }

  private void close(Closeable in) {
    if (in != null) {
      try {
        in.close();
      } catch (IOException e) {
        getExceptionListener().exceptionThrown(e);
      }
    }
  }

  private boolean parsingComplete() {
    if (this.input == null) {
      return false;
    }
    if (this.array == null) {
      if ((this.acc == null) && (null != System.getSecurityManager())) {
        throw new SecurityException("AccessControlContext is not set");
      }
      AccessController.doPrivileged(new PrivilegedAction<Void>() {
        public Void run() {
          XMLDecoder.this.handler.parse(XMLDecoder.this.input);
          return null;
        }
      }, this.acc);
      this.array = this.handler.getObjects();
    }
    return true;
  }

  /**
   * Sets the exception handler for this stream to <code>exceptionListener</code>.
   * The exception handler is notified when this stream catches recoverable
   * exceptions.
   *
   * @param exceptionListener The exception handler for this stream; if <code>null</code> the
   * default exception listener will be used.
   * @see #getExceptionListener
   */
  public void setExceptionListener(ExceptionListener exceptionListener) {
    if (exceptionListener == null) {
      exceptionListener = Statement.defaultExceptionListener;
    }
    this.handler.setExceptionListener(exceptionListener);
  }

  /**
   * Gets the exception handler for this stream.
   *
   * @return The exception handler for this stream. Will return the default exception listener if
   * this has not explicitly been set.
   * @see #setExceptionListener
   */
  public ExceptionListener getExceptionListener() {
    return this.handler.getExceptionListener();
  }

  /**
   * Reads the next object from the underlying input stream.
   *
   * @return the next object read
   * @throws ArrayIndexOutOfBoundsException if the stream contains no objects (or no more objects)
   * @see XMLEncoder#writeObject
   */
  public Object readObject() {
    return (parsingComplete())
        ? this.array[this.index++]
        : null;
  }

  /**
   * Sets the owner of this decoder to <code>owner</code>.
   *
   * @param owner The owner of this decoder.
   * @see #getOwner
   */
  public void setOwner(Object owner) {
    this.owner = owner;
  }

  /**
   * Gets the owner of this decoder.
   *
   * @return The owner of this decoder.
   * @see #setOwner
   */
  public Object getOwner() {
    return owner;
  }

  /**
   * Creates a new handler for SAX parser
   * that can be used to parse embedded XML archives
   * created by the {@code XMLEncoder} class.
   *
   * The {@code owner} should be used if parsed XML document contains
   * the method call within context of the &lt;java&gt; element.
   * The {@code null} value may cause illegal parsing in such case.
   * The same problem may occur, if the {@code owner} class
   * does not contain expected method to call. See details <a
   * href="http://java.sun.com/products/jfc/tsc/articles/persistence3/">here</a>.
   *
   * @param owner the owner of the default handler that can be used as a value of &lt;java&gt;
   * element
   * @param el the exception handler for the parser, or {@code null} to use the default exception
   * handler
   * @param cl the class loader used for instantiating objects, or {@code null} to use the default
   * class loader
   * @return an instance of {@code DefaultHandler} for SAX parser
   * @since 1.7
   */
  public static DefaultHandler createHandler(Object owner, ExceptionListener el, ClassLoader cl) {
    DocumentHandler handler = new DocumentHandler();
    handler.setOwner(owner);
    handler.setExceptionListener(el);
    handler.setClassLoader(cl);
    return handler;
  }
}
